Apparatus for applying a metal coating to an elongated metal article

ABSTRACT

An apparatus for applying a metallic coating to an elongated metal article. The article to be coated is transported through an enclosure with closure gates at the ends. A source of ionized metallic atoms is positioned around the article. Also within the enclosure is a tubular deflection screen at a potential which is of the same polarity as the ionized atoms. The deflector screen deflects back towards the article the ionized atoms produced by the source which do not strike the article when emitted by the source.

United States Patent Delcour et al.

[ 1 Sept. 26, 1972 154] APPARATUS FOR APPLYING A METAL COATING TO ANELONGATED METAL ARTICLE [72] Inventors: Leon Joseph Eugene Deleour,Liege; Dominique Thomas Francois Streel, I Cointe-Sclessin, both ofBelgium [73] Assignee: Cockerill-Ougree-Providence Et Esperance-Longdoz,en abrege Cockil .stre n l Belgium [22] Filed: Feb. 10, 1970 [21]Appl.No.: 10,169

[30] Foreign Application Priority Data Feb. 24, 1969 Belgium ..42,121

[52] US. Cl ..118/49.5,.118/634 [51] Int. Cl ..C23c 13/12 [58] Field ofSearch ..1 18/48-495; 117/93.4 R, 107.1

[56] References Cited UNITED STATES PATENTS 1,710,747 4/1929 Smith"118/49 UX 2,437,606 3/1948 Kaufman 17/9344 X 2,994,618 8/1961 Landgraf"117/9344 3,000,752 9/1961 Jackson et a1. 17/9344 X 3,192,892 7/1965Hanson et a1 ..l18/49.1 3,250,694 5/1966 Maissel et al.18/49.1 UX3,324,825 6/l967 Brumfield ..1 18/49.5

3,361,591 1/1968 Dill et al. ..l 18/49 .l X 3,395,674 8/l968 Burham eta1. ..l18/49.l 3,432,335 3/1969 Schiller et al. ..l...1 17/107. 1 X

2,382,432 8/1940 McManus et al. ..1 18/49 X 2,206,509 7/1940 Lederer ..ll8/49 X 3,288,638 11/1966 Van Paassen et al..l l8/49.1 X 3,386,9096/1968 Hough ..l 18149.5 X 2,621,624 12/1952 Chilowsky ..1 18/49 X2,771,568 11/1956 Steigerwald ..1 18/49 X 3,556,048 1/1971 Frazer ..ll8/49.5

FOREIGN PATENTS OR APPLICATIONS 665,540 9/1938 Germany ..1 18/49 PrimaryExaminer-Morris Kaplan Attorney-Sughrue, Rothwell, Mion, Zinn & Macpeak[5 7] ABSTRACT An apparatus for applying a metallic coating to anelongated metal article. The article to be coated is transported throughan enclosure with closure gates at the ends. A source of ionizedmetallic atoms is positioned around the article. Also within theenclosure is a tubular deflection screen at a potential which is of thesame polarity as the ionized atoms. The deflector screen deflects backtowards the article the ionized atoms produced by the source which donot strike the article when emitted by thesour e 7 v 1 1 Claims, 3Drawing Figures APPARATUS FOR APPLYING A METAL COATING TO AN ELONGATEDMETAL ARTICLE This invention relates to apparatus for applying to anelongated metal article a metallic coating obtained by condensation ofmetallic atoms produced by evaporation under vacuum of a metal heated toa temperature above its vaporization point.

It is known to protect the surfaces of metallic articles againstcorrosion by agents to which they are exposed, for the purpose ofextending their useful life; for exam ple, steel or articles made ofsteel may be protected against corrosion by means of various coatingsusing various methods.

At the present time, the apparatus most in demand have to be simple,reliable, economic and must provide uniform layers which are not verythick, adhere well and are resistant to corrosion.

One known apparatus provides for metallization under vacuum, includingplacing the articles to be coated in an enclosure where there is avacuum of approximately -4 Torr, into which enclosure, there areintroduced metallic vapors constituted by the atoms of the metalrequired to form the coating, these atoms being produced by evaporationof the metal heated to a temperature above its vaporization point sothat the vapors formed condense on the article to be coated.

This apparatus has the advantages that the coating obtained ishomogeneous and adhesive and can be composed of an alloy, and that themethod makes it possible to avoid the formation of fragile layers at theinterface between the article and the coating.

However, several disadvantages then became apparent, due to the factthat in the high vacuum provided, the atoms arrange themselves in alldirections along trajectories which may be considered as rectilinear.The atoms coming from source thus are arranged in the manner of luminousrays, and only those which directly strike the face of the article to becoated, i.e. visible from the source, contribute to the formation of thecoating, whereas all the others are lost and are deposited on adjacentparts of the apparatus, where they condense. The non-visible surfaces ofthe articles receive some lost atoms, but the coating thus formed isquite inadequate, necessitating one subsequent orientation of thesesurfaces towards the source of atoms.

As a result, there is a considerable loss of vaporized metal, resultingin a low yield and the need to present two faces of an article to becoated successively to the source of atoms. In particular, for thecoating of sheet strips this requirement means the construction of aplant of great length, and the machine has to be stopped frequently.

Moreover, when it is a matter of treating objects such as wires whichpresent a small surface to the source, the yield is particularly low.

The present invention aims at overcoming or reducing the effect of thesedisadvantages.

The present invention consists in an apparatus for applying to anelongated metal article, for example a steel article such as a strip ora wire, a coating obtained by condensation of the metallic atomsproduced by evaporation under vacuum of a metal heated to a temperatureabove its vaporization point, wherein the said article is arrangedvertically in an enclosure under a vacuum of 10'] to 10 5 Torr, a sourceof metallic atoms is arranged around the article and metallic atoms fromthe source having passed the article and thus not directly condensed onthe article, are deflected back towards the article.

In this way, it is possible to recover atoms which have escapedcondensation on the article to be coated and to redirect them towardsthe article after deflection on a screen. In this manner the yield ofthe coating operation is considerably increased, and thus the method isparticularly suitable for certain metallic products such as strips,rods, wires, i.e. elements having one dimension much larger than theother two, which, in the specification which follows, will be calledelongated metallic articles.

In the accompanying drawings:

FIG. 1 is a diagrammatic view of one form of apparatus constructed inaccordance with the present invention,

FIG. 2 is a partial diagrammatic view in perspective of the apparatus ofFIG. 1,

FIG. '3 is a view in perspective of a portion of a modified form ofapparatus for coating wire.

In carrying the invention into effect according to one convenient modeby way of example, FIGS. 1 and 2 show an apparatus for applying ametallic coating to a strip of sheet, which includes an enclosure 1arranged vertically, i.e. whose longitudinal axis is vertical, the twoends being closed by closure gates 2 and 3. Vacuum pumps, which are notshown, are attached to the said enclosure 1 and create there a vacuumgenerally of approximately 101 to 10-5 Torr. In this enclosure, ametallic strip 4, for instance of steel, transported by drive cylinders5 and 6 over a vertical path from the bottom of the enclosure to thetop. Two crucibles 7 and 8 composed of refractory material are locatedone on each side of the strip 4, the free side of each crucible beingina plane perpendicular to the strip 4. The crucibles contain a metalwhich by two electron guns 9 and 10, is raised to a temperature which ishigher than its vaporization point. The crucibles are suppliedcontinuously with metal by means of a cone device, which is not shown.The electron guns 9 and 10 which may be of a known type are providedwith a deflection system effecting a deflection of on the electrons anda reciprocating sweeping device to cause the electron to passalternately to each end of the crucibles, which ends are thus heatedequally. In this manner the crucibles constitute a source of metallicatoms, which when emitted follow paths which are almost rectilinear, andsome of them strike directly the two faces of the strip 4 where theycondense and form a coating. The atoms which do not reach the stripdirectly, pass to one side of it and strike the internal surface 11a ofa reflecting screen 11 forming a hood. This hood is brought to atemperature, called deflection temperature, by means of heating providedby a heating resistance 12 surrounding the hood and supplied from asource of current 13. The deflection temperature is selected in such amanner that the metallic atoms which strike the hood cannot condensethere and are immediately deflected towards the strip 4 which is to becoated. Tests which have been carried out have shown that in generalthis temperature may be between seven-tenths and twelve-tenths of thevalue of the melting point of the coating metal. The best manner ofoperation in practice is to perform tests by subjecting the hoodsuccessively to various increasing temperatures from a valueapproximately equal to threequarters of the vaporization temperature ofthe metal, and to determine that which supplies the best yield.

Alternatively, deflector screen 1 1 may be heated in a totally differentmanner by passing an electrical current through it so that its ownresistance brings about the heating. As a further alternative electronguns may be used, which may be the same guns for heating the crucibles,beams of electrons issuing from the guns being moved such that in turnthey strike against the crucibles and the internal surface of thescreen. Moreover, the heating of the screen by a particular means mayeven be omitted, since when the apparatus is operating, the cruciblesheated by the electron guns emit thermal radiation sufficing in certaincases to heat surface with parabolic directrix.

Moreover, the hood 11 is connected by a circuit 14a to the positive poleof a source of current 14 and the metallic atoms emitted are subjectedon issuing from the crucibles to the action of an ionization device 15of a known type arranged immediately above the crucibles. Accordinglythe atoms are transformed into positive metallic ions which by virtue ofthis device are repelled by the positive hood and returned to the strip4 where they condense, which increases the yield. The' yield may bestill further increased by connecting the strip 4 to the negative poleof a source of current, not shown. The value-of the potentials of thestrip and of the hood depend in particular on the nature of the metaldeposited and the operating conditions. Thus, for depositing nickel, ithas been found that the strip should be at approximately 500V, the hoodat approximately 100V and the vaporized nickel at earth potential.

Although this is not always necessary, in certain cases to ensureperfect adherence of the coating, the article may be heated to atemperature in general between one-fifth and-one-third of the meltingpoint of the metal to be deposited. Thus, in FIG. 1, this heating of thestrip 4 is obtained by a source of current 16 connected by conductors 17to the cylinders 5 and 6 driving the strip 4, which is thus heated bythe Joule effect. The heating of the strip 4 may also be obtained by anelectron gun 22 as shown in FIG. 2.

For the application of a metallic coating on a metallic wire, forinstance of steel, use can be made of apparatus such as that partiallyillustrated in FIG. 3. In this case, the hood 18 forming the deflectorscreen has a cylindrical/conical shape and its opening 180 is directeddownwardly. Following its axis, a wire 19 to be covered passes alongtoissue through the apex 18b, driven by a device not shown, analogous tothe cylinders 5 and 6. Two crucibles 20 of semi-toroidal shape surroundthe wire 19 and each is swept alternately first in one direction andthen in the other by the electrons emitted by two electron guns 21 anddeflected by a known device which is not shown. I

The apparatus of FIG. 3 also has an enclosure for the hood, a device forheating and polarizing the hood, a heating device for the wire, anionization device for the metallic atoms, as in the apparatus shown inFIGS. 1 and 2 provided for coating a metallic strip.

The advantage of the apparatus is that it applies simultaneously auniform coating on the two sides of an extended metallic product such asa strip, a wire or a section of metal. Moreover, the yield is'increasedand there is far less clogging of the apparatus, with the result thatthere are far fewer stoppages for cleaning and production is increased.1

What we claim is: r

1. An apparatus includingan enclosure for applying ametallic coating toan elongated metal article said apparatus comprising:

a. closure gates at each end of the enclosure;

b. transporting means for transporting said elongated metal articlethrough the enclosure along a vertical P 0. source means for producingmetallic atoms, the

source means being positioned around the elongated metal article in aplane normal to the path;

d. ionizing means for ionizing the atoms produced by said source means;

e. tubular deflector screen means, surrounding in part the articlepassing therethrough for deflecting back towards the elongated metalarticle the metallic atoms which have passed to the side of theelongated metal article and have not condensed thereon, wherein thedeflector screen means is positioned above the source means;

f. a dc. current source having one pole connected to the deflectorscreen means for applying a potential to said screen means which is ofthe same polarity as the polarity of i said ionized atoms therebyenhancing the deflection by said screen means; and:

g. means for creating a vacuum of from 10-1 to 10'5 Torr within theenclosure.

2. Apparatus as claimed in claim 1,- wherein the deflector screen meansis arranged to be heated.

3. Apparatus as claimed in claim 2, wherein the deflector screen meansis raised to a temperature eq ual to at least to seven-tenths. of thetemperature of vaporization of the metal producing the metallic atoms.

4. Apparatus as claimed in claim 1, wherein the deflector screen meansis defined by the internal surface of a geometrical body with edges.

5. Apparatus as claimed in claim 1, wherein the a source means ofmetallic atoms comprises at least one crucible'containing the metal tobe vaporized under, said apparatus further including an electron gun forvaporizing the metal.

9 Apparatus as claimed in claim 1 wherein the section in the horizontalplane. deflector screen means is defined by the internal sur- T eapparatus 88 Set forth n C aim 1 herein Said face of a body ofrevolution. tubular deflector screen means has a circular cross sec- 10.The apparatus as set forth in claim 1 wherein said m the horizontal Ptubular deflector screen means has a rectangular cross 5

1. An apparatus including an enclosure for applying a metallic coatingto an elongated metal article said apparatus comprising: a. closuregates at each end of the enclosure; b. transporting means fortransporting said elongated metal article through the enclosure along avertical path; c. source means for producing metallic atoms, the sourcemeans being positioned around the elongated metal article in a planenormal to the path; d. ionizing means for ionizing the atoms produced bysaid source means; e. tubular deflector screen means, surrounding inpart the article passing therethrough for deflecting back towards theelongated metal article the metallic atoms which have passed to the sideof the elongated metal article and have not condensed thereon, whereinthe deflector screen means is positioned above the source means; f. ad.c. current source having one pole connected to the deflector screenmeans for applying a potential to said screen means which is of the samepolarity as the polarity of said ionized atoms thereby enhancing thedeflection by said screen means; and g. means for creating a vacuum offrom 10 1 to 10 5 Torr within the enclosure.
 2. Apparatus as claimed inclaim 1, wherein the deflector screen means is arranged to be heated. 3.Apparatus as claimed in claim 2, wherein the deflector screen means israised to a temperature equal to at least to seven-tenths of thetemperature of vaporization of the metal producing the metallic atoms.4. Apparatus as claimed in claim 1, wherein the deflector screen meansis defined by the internal surface of a geometrical body with edges. 5.Apparatus as claimed in claim 1, wherein the source means of metallicatoms comprises at least one crucible containing the metal to bevaporized under, said apparatus further including an electron gun forvaporizing the metal.
 6. Apparatus as claimed in claim 5, furtherincluding means for moving the stream of electrons issuing from the saidelectron gun in a to and fro movement.
 7. Apparatus as claimed in claim5, wherein the crucible containing the metal has the form of a ring. 8.Apparatus as claimed in claim 1, wherein the deflector screen means hasa cylindrical/conical shape.
 9. Apparatus as claimed in claim 1 whereinthe deflector screen means is defined by the internal surface of a bodyof revolution.
 10. The apparatus as set forth in claim 1 wherein saidtubular deflector screen means has a rectangular cross section in thehorizontal plane.
 11. The apparatus as set forth in claim 1 wherein saidtubular deflector screen means has a circular cross section in thehorizontal plane.